Inclusion Criteria: * Documented GM1 gangliosidosis diagnosis based on genotyping confirming the β-gal gene mutations and/or documented deficiency of β-gal enzyme by laboratory testing * Children with early infantile GM1 gangliosidosis less than 12 months of age with ability to swallow * Children with late infantile GM1 gangliosidosis less than 3 years of age with ability to sit Exclusion Criteria: * Uncontrolled seizure disorder. Patients who are stable on anti-convulsive medications may be included * More than 40% brain atrophy as measured by MRI total brain volume at screening * Current participation in a clinical trial of another investigational medicinal product * Past participation in a gene therapy trial * History of hematopoietic stem cell transplantation * Any condition that would contraindicate treatment with immunosuppressant therapy * Presence of concomitant medical condition or anatomical abnormality precluding lumbar puncture or intracisternal injection * Presence of any permanent items (e.g., metal braces) precluding undergoing MRI * History of non-GM1 gangliosidosis medical condition that would confound scientific rigor or interpretation of results * Rare and unrelated serious comorbidities, e.g., Down syndrome, intraventricular hemorrhage in the new-born period, extreme low birth weight (\<1500 grams) or known bleeding disorders * Any vaccination 1 month prior to the planned immunosuppressant treatment * Serology consistent with HIV exposure or consistent with active hepatitis B or C infection * Grade 2 or higher lab abnormalities for Liver function tests (LFT), bilirubin, creatinine, hemoglobin, white blood cell (WBC) count, platelet count, prothrombin time (PT), and partial thromboplastin time (PTT), according to CTCAE v5.0